1. Field of the Invention
The invention relates to a thrust ball bearing cage. The invention also relates to a thrust ball bearing.
2. Description of Related Art
As a conventional thrust ball bearing cage (hereinafter referred to as a cage), there is a cage described in Japanese Patent Application Publication No. 2008-223970 (FIG. 3 in JP 2008-223970 A). The cage is formed of an annular member, and the annular member has a plurality of pockets arranged at intervals and extending through the annular member in an axial direction
Each pocket has a plurality of claw-shaped protrusions, and the claw-shaped protrusions protrude at a periphery of an opening of the pocket so as to be formed in a convex shape. The claw-shaped protrusions are arranged at intervals at the periphery of the opening of the pocket. The axial height of each claw-shaped protrusion is increased as the claw-shaped protrusion gets closer to a center of the pocket from a radially outer end of the cage. The claw-shaped protrusions are provided so as to hold balls, thereby preventing the balls from coming out of the pockets.
The inventor found that the conventional cage had the following problems.
In the case of the conventional cage, the claw-shaped protrusions are less likely to be elastically deformed. When the balls are fitted in the pockets, the balls and the claw-shaped protrusions are therefore brought into contact with each other, whereby the claw-shaped protrusions are likely to be damaged.
In addition, in the conventional cage, the axial height of the claw-shaped protrusion is increased as the claw-shaped protrusion gets closer to the center of the pocket from the radially outer end of the cage. Lubricant is therefore less likely to be retained in the vicinity of the pockets. As a result, the lubricant is less likely to reach a sliding portion such as an inner face of the pocket.